Method and apparatus for keeping free the agitator shaft seals from polymeride in polymerization vessels with bottom drive

ABSTRACT

A method and apparatus for keeping an agitator shaft seal free from polymeride in polymerization vessels with bottom drive and contents in excess of 20 m3, in which a flushing liquid is supplied from the outside into the channel connecting the mechanical seal of the agitator shaft with the vessel interior space, whereby the liquid reaches the vessel interior space from the connecting channel with an average minimum velocity of about 20 cm/sec.

[451 Jan. 1,1974

[56] References Cited UNITED STATES PATENTS METHOD AND APPARATUS FORKEEPING FREE THE AGITATOR SHAFT SEALS FROM POLYMERIDE IN POLYMERIZATIONVESSELS WITH BOTTOM DRIVE [75] Inventors: Herbert Kahanek; Karl-HeinzBiihmer; Willi Schiemann; Giinter Beckmann, all of Marl, GermanyChemische Werke Huls 5 2 W6 6 /2/ 77 7 27/7 A ---H- m m 2m mm m m T m mA m m C I m m h n P m m P L MA a m R a m W O am s T Q .l KSME m T 0281 A6647 P 9999 m wm N. 1 m E 85200 R 90400 0 35 F 5500 6 49 2323 911,55711/1962 Great Britain............... 259/DIG. 16

[73] Assignee:

Aktiengesellschaft, Marl, Germany Primary Examfner samu?l RothbergAttorney-Craig, Antonelll & H111 Apr. 21, 1971 [22] Filed:

[57] ABSTRACT A method and apparatus for keeping an agitator shaft sealfree from polymeride in p01 with bottom drive and contents in Appl. No.:135,865

ymerization vessels Foreign Application Priority Data excess of 20 m, in

Apr. 21, 1970 Germany................... P 20 19 017.4

which a flushing liquid is supplied from the outside into the channelconnecting the mechanical seal of the yey .wmh C r emI h e V Wr m ec CCmm m rr .mwm flaw ttr .mm a S n wm vv k t tt t 11C hS C .n fi6 argeommfi ru whim a nr m g owf at tco 8 Claims, 1 Drawing Figure PMENTEUJM 1I974 I Ill/I INVENTORS HERBERT KAHANEK KARL-HEINZ BUHMER w LLI SCHIEMANNGUNTER BECIKMANN ATTORNEYS BY mou METHOD AND APPARATUS FOR KEEPING FREETHE AGITATOR SHAFT SEALS FROM POLYMERIDE IN POLYMERIZATION VESSELS WITHBOTTOM DRiVE The present invention relates to 'a method and apparatusfor keeping free the agitator shaft seals from polymeride inpolymerization vessels with bottom drive and with contents in excess of20 m used for carrying out liquid-phase polymerizations of all types,especially of suspension and emulsion polymerizations such as that ofthe vinyl chloride or of the butadiene alone or with each other or alsowith other co-monomers, for example, of the emulsion polymerization ofbutadiene or styrol.

The polymerization reaction of vinyl chloride into polyvinylchloride iscarried out normally according to discontinuous or continuous processesin pressure-tight agitator vessels. The vinyl chloride and the polymerare thereby suspended in water or emulsified. One also carries out in asimilar manner in agitator vessels the emulsion polymerization ofbutadiene-styrol-mixture polymerides, of pure butadiene or also of othercomonomers with butadiene or vinyl chloride. The presently customaryvessels have contents of the order of 8 to 20 m These vessels includestirring or agitator members, for example, flat blade paddle agitators,im-v peller agitators or turbine agitators, which are secured at anagitator shaft extending through the vessel hood. For the most part, theagitator shaft is sealed at the hood by a double-acting mechanical sealring packing or seal.

Since the need for polymerides increases constantly, there exists thenecessity to establish high output production .lines or facilities withthe use of large polymerization vessels. With the construction ofvessels, whose content or volume is larger than 20 m one encountersgreat difficulties in connection with the dimensioning of the agitatorshaft. With a polymerization vessel having a volume of 50 m for vinylchloride with an impeller agitator arranged above the vessel bottom, theagitator shaft extending through the vessel hood would have tobeconstrucfedat lea st with a diameter of 300 mm. in order that the strongdrive torque can be transmitted vibration-free to the agitating element.With agitating shafts constructed too thin, the shaft gets into strongflexural or bending vibrations by reason of the unavoidablealternatingforces acting on the agitator element, which may lead to thefracture or buckling of the shaft. An unintentional stoppage orinterruption of the agitating operation may cause serious operationaldisturbances.

The agitator shafts with more than 250 mm. diameter are expensive, heavyand difficult to assemble. They necessitate mechanical seals for thesealing thereof which are extraordinarily costly both in the initialacquisition as also in the subsequent maintenance.

Consequently, it appears reasonable to drive the agitator element fromthe vessel bottom by means of a socalled bottom drive. The agitatorshaft could thereby be extremely short and would therefore be hardlyendangered by bending or flexure vibrations even with a slenderconstruction.

Constructions of polymerization vessels with bottom drive are known assuch. However, they are not suited for the realization of all types ofpolymerizations or copolymerizations in liquid phase.

In particular, these constructions are not suited for suspension andemulsion polymerizations such as that of the vinyl chloride or of thebutadiene alone or also with other co-monomers, for example, of theemulsion copolymerization of butadiene and styrol, because polymerideforms during the reaction in the ringshaped channel, which leads fromthe vessel interior space to the mechanical seal ring, whereby thepolymeride after a certain time presses apart the two mechanical sealrings sliding one upon the other, which provide a seal in the directiontoward the vessel interior space, and permits the blocking oil to enterinto the vessel.

The present invention is concerned with the task, for the realization ofthe polymerizations or copolymerizations in polymerization vessels witha volume in excess of 20 m to render the seal of the bottom drive ofagitating units durable.

The underlying problems are solved according to the present invention inthat a flushing liquid compatible with the polymerization startingformulation is introduced from the outside into the annularly shapedchannel connecting the mechanical seal of the agitator shaft with thevessel interior space and from there reaches the vessel interior spacewith a minimum velocity of 20 cm/sec.

The advantages achieved by the present invention essentially consist inthat the mechanical seals of the agitator shaft do not come into contactwith the suspension or emulsion of the vessel filling, remain free frompolymeride fully operational and therewith enable the safe use of thebottom drive with polymerizations or copolymerizations in polymerizationvessels with a volume in excess of 20 m Accordingly, it is an object ofthe present invention to provide a polymerization method and apparatuswhich avoid the aforementioned shortcomings and drawbacks in connectionwith large-size polymerization vessels.

Another object of the present invention resides in a method andapparatus for keeping the agitator shaft seals free from polymeride inpolymerization vessels with bottom drive and of relatively largecontents.

A further object of the present invention resides in a polymerizationvessel with bottom drive and a content in excess of 20 m which permits along length of life of the agitator shaft seals.

These and further objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illustration only, one embodiment in accordance with thepresent invention, and wherein: The single FIGURE is a somewhatschematic crosssectional view through a polymerization vessel withbottom drive and agitator shaft seals in accordance with the presentinvention.

Referring now to the single FIGURE of the drawing, the shaft seal at thebottom of a polymerization vessel of a size of about 40 m is illustratedin this FIGURE. The agitator shaft 1 is sealed by means of adoubleacting mechanical seal ring 2 of conventional construction. Thering-shaped channel 4, which forms the space between the mechanical seal2 and the vessel interior space 5, is supplied from the outside with theflushing liquid by way of the capillary pipe line 3 provided in themechanical seal housing 2a; the flushing liquid subsequently flows outof the ring-shaped channel 4 into the vessel interior space in themanner to be described more fully hereinafter.

It has now been discovered that the velocity of the flushing liquidentering into the vessel interior space 5 must not fall below apredetermined value if the penetration of polymerizing emulsified ordispersed substances into the ring-shaped channel 4 in the directiontoward the sliding ring seal is to be prevented. It has been discoveredthat the value of this minimum velocity amounts to about 20 cm/sec.,measured as an average value over the cross section of the inletaperture into the vessel interior space.

In order not to reduce in a non-permissive manner the concentration ofthe substance to be polymerized or of the polymeride within the vessel,one should feed into the vessel as little flushing liquid as possible.

These requirements and the relatively high minimum velocity of 20cm/sec. produce together the necessity to constitute the inlet openingof the flushing liquid into the vessel interior space 5 as narrow aspossible, i.e., therefore gap-shaped. This may be realized by means ofan insert which is mounted in the space between the mechanical seal andthe vessel interior space, or with the aid of a possibly multi-partiteor adjustable collar mounted above this intermediate space or of anyother element, effecting a constriction of the flushing liquid dischargein the direction toward the vessel interior space.

In the embodiment of the present invention illustrated in FIG. 1, anadjustable cap 6 constructed as axially symmetrical body is mounted onthe agitator shaft 1 above the ring-shaped channel 4, which leaves openin the direction toward the vessel interior space 5 an annularly shapedgap 7 above a plate 9 having a surface ground flat and inserted into thevessel casing or jacket 8. The height of the gap 7 can be adjusted bythe adjustment of the cap 6 in any conventional manner. The smallestpossible gap height depends on the precision of the shaft bearing, onthe fitting tolerances, on the manufacturing accuracies and the shaftbending.

With the increase of the vessel volume, the ratio of the shaft diameterand of the gap height decreases and therewith also the ratio of thefed-in flushing liquid quantity to volume. Thus, the possiblyundesirable decrease of the concentration of the substances to bepolymerized or of the polymeride in the vessel is decreased thereby.

The following example which is non-limitative of the present invention,represents typical values for a method and apparatus of this invention.

EXAMPLE Vinyl chloride suspended in water was polymerized in thepolymerization vessel with bottom drive and with a volume of 40 m at anoperating pressure of 8 atu and at a temperature of 60 C. under constantstirring or agitation. The agitating shaft had a diameter of 245 mm. androtated with 80 rotations per minute. 260 l/h of water was fedcontinuously into the vessel interior space in the course of apolymerization duration of 10 hours through an annularly shaped gap of300 mm. diameter and a gap height adjusted to 0.3 mm. The velocity ofthe water flowing through the ring-shaped gap amounted to 25 cm/sec. Thereduction of the vinyl chloride or polyvinylchloride concentrationamounted to 0.027 percent. The mechanical seals were free frompolymeride and undamaged after polymerization charges.

While we have shown and described only one embodiment in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

We claim:

1. An apparatus for keeping agitator shaft seal means free frompolymerization vessels with bottom drive means and with relatively largevolume, characterized by slide ring seal means for the agitator shaft,ringshaped channel means connecting the slide ring seal means with thevessel interior space, first means for continuously supplying a flushingliquid from the outside into said channel means, and second meansproviding a restricted discharge opening of said channel means into thevessel interior space for continuously discharging the flushing liquidfrom said channel means into the vessel interior space at apredetermined average minimum velocity of about 20 cm/sec.

2. An apparatus according to claim 1, characterized in that said firstmeans includes a capillary pipe line provided in a mechanical sealhousing which leads from the outside to said ring-shaped channel means.

3. An apparatus with a vessel casing according to claim 2, characterizedin that the second means effecting the constriction of the liquiddischarge is a cap constructed as substantially axially symmetricalelement which is adjustable on the agitator shaft in the vessel interiorspace above the channel means and leaves open a ring-shaped gap above aplate with flat ground surface inserted into the vessel casing.

4. An apparatus for keeping agitator shaft seal means free frompolymeride in polymerization vessels with bottom drive means and withrelatively large volumes, characterized by slide ring seal means for theagitator shaft, ring-shaped channel means connecting the slide ring sealmeans with the vessel interior space, first means for supplying aflushing liquid from the outside into said channel means, and secondmeans providing a restricted discharge for the flushing liquid from thesaid channel means into the vessel interior space, said first meansincluding a capillary pipe line provided in a slide ring seal housingwhich leads from the outside to said ring-shaped channel means.

5. An apparatus with a vessel casing according to claim 1, characterizedin that the second means effecting the constriction of the liquiddischarge is a cap constructed as substantially axially symmetricalelement which is adjustable on the agitator shaft in the vessel interiorspace above the channel means and leaves open a ring-shaped gap above aplate with flat ground surface inserted into the vessel casing.

6. An apparatus according to claim 1, characterized in that the volumeof the vessel is in excess of about 20 m 7. An apparatus according toclaim 4, characterized in that the volume of the vessel is in excess ofabout 20 m 8. An apparatus according to claim 4, characterized in thatthe first and second means provide a predetermined average minimumvelocity of about 20 cm/sec for the flushing liquid at the discharge ofthe flushing liquid from the channel means into the vessel interiorspace.

1. An apparatus for keeping agitator shaft seal means free fromPolymerization vessels with bottom drive means and with relatively largevolume, characterized by slide ring seal means for the agitator shaft,ring-shaped channel means connecting the slide ring seal means with thevessel interior space, first means for continuously supplying a flushingliquid from the outside into said channel means, and second meansproviding a restricted discharge opening of said channel means into thevessel interior space for continuously discharging the flushing liquidfrom said channel means into the vessel interior space at apredetermined average minimum velocity of about 20 cm/sec.
 2. Anapparatus according to claim 1, characterized in that said first meansincludes a capillary pipe line provided in a mechanical seal housingwhich leads from the outside to said ring-shaped channel means.
 3. Anapparatus with a vessel casing according to claim 2, characterized inthat the second means effecting the constriction of the liquid dischargeis a cap constructed as substantially axially symmetrical element whichis adjustable on the agitator shaft in the vessel interior space abovethe channel means and leaves open a ring-shaped gap above a plate withflat ground surface inserted into the vessel casing.
 4. An apparatus forkeeping agitator shaft seal means free from polymeride in polymerizationvessels with bottom drive means and with relatively large volumes,characterized by slide ring seal means for the agitator shaft,ring-shaped channel means connecting the slide ring seal means with thevessel interior space, first means for supplying a flushing liquid fromthe outside into said channel means, and second means providing arestricted discharge for the flushing liquid from the said channel meansinto the vessel interior space, said first means including a capillarypipe line provided in a slide ring seal housing which leads from theoutside to said ring-shaped channel means.
 5. An apparatus with a vesselcasing according to claim 1, characterized in that the second meanseffecting the constriction of the liquid discharge is a cap constructedas substantially axially symmetrical element which is adjustable on theagitator shaft in the vessel interior space above the channel means andleaves open a ring-shaped gap above a plate with flat ground surfaceinserted into the vessel casing.
 6. An apparatus according to claim 1,characterized in that the volume of the vessel is in excess of about 20m3.
 7. An apparatus according to claim 4, characterized in that thevolume of the vessel is in excess of about 20 m3.
 8. An apparatusaccording to claim 4, characterized in that the first and second meansprovide a predetermined average minimum velocity of about 20 cm/sec forthe flushing liquid at the discharge of the flushing liquid from thechannel means into the vessel interior space.